Quality characteristics of harvested rainwater from galvanized roofing sheet in Esan West, Edo State

Abstract

Direct rainwater harvesting (DRWH) from rooftop is an important alternative source of water supply for both rural and semi-urban populace in developing countries to meet the increasing demand for domestic purposes. Nevertheless, the quality of this water supply source is of utmost importance as the health condition of water is a determinant of community health status. The aim of this research is to investigate the quality of harvested rainwater as an alternative source of drinking water in rural areas of Esan West Local government areas, Edo State. The Local Government Area was delineated into its already existing ten (10) political wards. Households were randomly selected and rainwater samples were collected during rainfall events for two sampling periods; onset and peak of rainfall via rooftop runoff with the aid of pre-sterilized plastic containers connected to the selected rooftops. Two (2) control (ambient rainwater) samples were also collected directly from rain drop without contact with any roof material. Water samples were analyzed for physical, chemical and bacteriological characteristics using standard method for the examination of water. The examination of physical parameters showed no evidence of water pollution as samples collected had values below the WHO permissible limits. Notwithstanding there was indication that harvested rainwater were slightly acidic. The examination of chemical parameters showed that Calcium ion (Ca²⁺) exceeded WHO permissible limits, while heavy metals (Fe, Pb, Cr) showed no pollution in all samples collected as they were within WHO permissible limits. Bacteriological qualities of samples showed evidence of contamination which is likely to be either from dust or bird, lizard, and squirrel droppings. Escherichia coli (E. coli) was isolated from almost all the samples considered. The two rainfall periods (onset and peak of rain) showed marked difference in the quality of water harvested. Water samples collected at the peak of rain had better water quality than these collected at the onset of the rain. However, the rainwater harvested at the peak of rain did contain some contaminants at levels above WHO drinking water standards such as TCC and E. Coli. This implies the need for treatment of harvested rainwater before domestic use.

Keywords: Water quality, galvanized rooftop sheet, rainwater runoff, rainwater harvesting